This invention relates to a cermet alloy superior in toughness, chipping resistance and high-temperature strength.
Hitherto, components such as Mo.sub.2 C, WC, TaC and NbC have been added to cermet alloys in order to improve wetting between a metal binding phase and TiC particles or TiCN particles which are main components of cermet alloys. These additive components surround TiC or TiCN particles through dissolution into binding phase and precipitation onto TiC or TiCN particles during sintering to form a rim portion, and in a cermet with a binding metal phase, generally the composite carbo-nitride has a rim-and-core structure, but the central portion, i.e., core portion is rich in Ti and nitrogen and then, the rim portion is rich in wetting improving components such as WC, TaC, Mo.sub.2 C and NbC and poor in Ti and nitrogen.
Formation of the rim portion improves wetting between the TiC or TiCN particles and metal binding phase, resulting in improvement in toughness, but with formation of the rim portion, particles of the composite carbo-nitride grow and they come to contact with each other. This portion where the composite carbo-nitride particles in contact with each other becomes a source for generation of micro-cracks or is apt to cleave as a path for propagation of cracks upon application of external stress, whereby chipping resistance is deteriorated. When the amount of the components which form the rim portion is decreased, toughness and high-temperature strength are deteriorated and overall characteristics are deteriorated. Thus, at present, addition of the rim portion forming components in more than a certain amount cannot be avoided.